2,642. Forgetting the Object of One's Oath

Hilchos Shevuos 3:9

Let’s say that someone took an oath not to eat wheat bread and he then ate wheat bread thinking that it was barley bread. Such a person is considered to have violated his oath due to circumstances beyond his control, and is therefore exempt, because he didn’t become unaware of his oath, he became unaware of the object of his oath.

Hilchos Shevuos 3:10

If one became unaware both of his oath and of the object of his oath, he is not liable to bring an offering. An example is if someone took an oath not to eat wheat bread and he thought he took an oath to eat wheat bread, plus he ate wheat bread thinking it was barley bread. This person is exempt because he became unaware of both his oath and the object of his oath, so he is considered to have violated due to circumstances beyond his control.